Flatback turtle

Flatback turtle hatchling Photo: H. Venz

Common name: Flatback turtle

Scientific name:Natator depressus

Family: Cheloniidae (sea turtles)

Conservation status: This species is listed as Vulnerable in Queensland (Nature Conservation Act 1992) and nationally (Environment Protection and Biodiversity Conservation Act 1999). It is ranked as a critical priority under the Department of Environment and Heritage Protection Back on Track species prioritisation framework.

Description

The flatback turtle is grey or pale grey-green or olive above and creamy-yellow below. The head of adults is a moderate size and the thick overlapping carapace scales form an oval to heart-shaped shell. Hatchlings are olive-green and the margins of the dorsal scutes are broadly outlined in black. Adults can grow to up to 1.2 metres in length (head to tail).

Habitat and distribution

Adult female flatback turtle Photo: C.J. Limpus

All known breeding sites of the flatback turtle occur in tropical Australia, on beaches and islands in Queensland, the Northern Territory and Western Australia. They feed in the northern coastal regions of Australia, ranging as far south as the Tropic of Capricorn. Their feeding grounds also extend to the Indonesian archipelago and the Papua New Guinea coast.

The Queensland Trust for Nature purchased Avoid Island, one of the three major breeding sites in eastern Australia for flatback turtles, and is working in partnership with the department to assess the island and establish a Nature Refuge. Once a Nature Refuge is in place the island can be on-sold while ensuring the conservation significance of the island is maintained in perpetuity.

Life history and behaviour

Flatback turtles lay the fewest eggs of any marine turtle, with approximately 50 eggs per nest buried under the sand. Hatchlings break through the leathery shell of the egg at night, before digging together through the sand to the surface. Once on the surface of the beach, the hatchlings orientate themselves towards the lighter horizon of the ocean and then move as fast as they can down the beach and into the waves.

Early life for the hatchlings is precarious, as many are eaten by sharks and crocodiles, with few making it to adulthood. The carapace (shell) of an adult flatback turtle can grow up to one metre long. Flatbacks prefer inshore waters where they can feed in shallow sea-beds on a carnivorous diet of soft-bodied marine life such as soft corals, sea cucumbers, and jelly-fish. They return to the region of their origin to breed, with females then laying their eggs on a nesting beach.

Threatening processes

Avoid Island Photo: Queensland Trust for Nature

All marine turtles are experiencing serious threats to their survival. Threats include:

Feral pigs are responsible for high levels of nest-predation with 90% of nests predated in west Cape York in the past. The pig's keen sense of smell allows them to locate buried turtle nests and subsequently dig up and consume all the contents.

Nesting beaches are also disturbed by vehicles and coastal development. Uncontrolled vehicles can damage nests and disturb laying turtles. Light pollution at night from shops and houses can disorientate hatchlings causing them to move inland where they are easy prey for other animals.

Pollution of waterways can impact on important turtle habitats, especially coral reefs.

Despite the use of TEDs (Turtle Excluder Devices) in the fishing industry, many flatback turtles still drown in fishing equipment, such as discarded nets (also known as ghostnets).

Recovery actions

In 2006 over 9000 feral pigs were culled on Cape York Peninsula. This has had huge benefits for the biodiversity of the Cape, including marine turtles. During the 2007 flatback nesting season on the western Cape York Peninsular there was reduced feral pig and wild dog predation on some beaches.

What can be done to help this species?

You can help this species by:

disposing of your rubbish appropriately. Remember that rubbish you throw away can find its way to the sea, where turtles can mistake things such as plastic bags for jellyfish. Plastic swallowed by mistake can cause blockages of the stomach and intestines of marine animals such as turtles;

being on the lookout to avoid turtles when out in your boat. Many turtles are struck by propellers of speeding boats and this can cause injury and death;

following the regulations relating to Personal Water Craft (jet skis, waveriders and waverunners), avoiding travelling over seagrass beds and shallow water, staying in the navigation channel when travelling in conservation zones and operating off the plane in "turtle and dugong go-slow areas".